For a holiday trip later this year with multiple flights (including a transfer at Dubai), I've been trying to find the best battery option to power my KX3, and came across these car start booster + power bank combinations. As they look and work like any ordinary USB power bank, which I'm sure the security clowns see hundreds of times a day, I figured that this would be the least problematic kind of power source to take on a flight, in a handy package with additional features (i.e. USB charging), and with the charger included as well.

I've ordered and tested four different devices; the results are below. All these devices have some things in common:

The 12 V output has an EC5 high current connector, commonly used for RC models, so readily available to make your own Powerpole adapter etc. It is directly connected to the internal LiPo battery to be able to supply the large currents necessary to start a car engine.

An adapter cable from EC5 to battery clamps is provided, and has a high-current fuse in its positive lead.

The internal battery is (apparently) a 3S LiPo – 12.5 V when fully charged, and around 11 V for most of the discharge time.

There is a USB output for charging mobile devices (usually 5 V/2 A), and a cable whip with multiple connectors for common smartphones etc. is supplied.

There is a built-in light function (bright white LED).

Dimensions are around 14 x 8 x 1.5 cm and the weight is about 200 g.

Test conditions:

Ambient temperature 23 °C.

After taking out of their packaging, the boosters were first fully charged, then fully discharged, then fully charged again before measuring the capacity.

Capacity measurements were taken by discharging through the EC5 connector from full down to 10 V (under load) at 2 A constant current. 10 V is the minimum voltage to get 10 W output from a KX3 with current firmware, and still more than high enough to be safe for a 3S LiPo.

The capacity of these devices is typically enough for 2-3 hours of SOTA CW operation with a KX3. I've used the first start booster listed in the results below (CP-02) during the activation of HB/SG-017 on 07/Aug/2017, making 73 QSOs over a period of two hours at 10 W, and it was still not drained afterwards (unfortunately I forgot to measure the remaining capacity before recharging it upon returning home). I plan on using the other devices on activations as well and add some more info about USB output QRM etc.

QRM: in practical SOTA operation (on a summit, KX3 powered from start booster, EFHW antenna connected), as expected there was no QRM whatsoever from the start booster if its USB output was not in use. While charging an iPhone, about S2 QRM could be heard on 10m SSB (vs. S0 with the booster off); on 20m and 40m, no difference in noise floor was heard whether the booster's USB function was on or off.

Verdict: seems to work very well!

Autostarter Fuel Slim

This one has an alumimum case, and although it is a bit heavier than the plastic alternatives, it has a high-quality feel to it. First booster delivered was DoA – could not be turned on or charged (voltage measured at "car" connector was 2.4 V, looks like the internal battery was completely drained and thus defective). I got a replacement, which worked fine.

NoName Chinese car jump starter

Many devices like this one can be found on eBay and AliExpress, under various brand names and in various colors. They all have the same case with the four charge state LEDs on the side and an oblong button next to them. Colors vary, as do the mAh ratings (which are of course ridiculously inflated). Whether the devices are all the same internally is not clear.

No cable/adapter to charge the start booster is supplied; the user is supposed to have their own Micro USB cable to charge the device through its Micro USB charging port. I first charged it using the USB port of my MacBook Pro, which worked, but the start booster got very hot around the charge input port, and there was a slight "burnt electronics smell". Nevertheless, it got fully charged after about two hours.

While using the USB output function, it emitted a high-pitch audible noise; probably a very cheap DC-DC converter (one can only imagine the kind of QRM it generates – though I didn't get around to measuring it before the device died). The device has a very cheap feel to it.

I discharged it down to "one LED", and then used a stronger USB power supply to recharge it, while also measuring the current this time. The device drew up to 5 Amps from the USB power supply, and soon smoke came out of the booster's charge input. After that, the USB charge/discharge circuitry was dead.

Either I got a faulty device, or the charger inside this device really does not have a current limit and relies on the USB power supply to be current-limited.

I took a normal USB 1S3P LiPo pack and rewired to be a 3S1P pack. The USB A plug is wired like a balancing connector so with a simple adaptor cable I have a SOTA battery I can have in my carry-on luggage that is completely normal in appearance. Claimed to be 2.8Ah pack but probably nearer 2Ah TBH.

See pictures on ebay : It can hold 4 cells (type 18650) you have to provide yourself, but they are not soldered in place.So I was going to make another battery holder to place the cells in series, to get 16V out This other battery holder would then go in checked luggage.I may still do it if airline regulations get any stricter.73 - Luc ON7DQ

The "5V-1A household charger" that was on the packing list on eBay was not included in the package. This start booster is charged through a Micro USB input. Recharging takes about 6 hours (it draws about 900 mA from the 5 V USB supply).